The present disclosure relates to turbomachinery, and more particularly, to adjustable seals for use in steam turbines.
At least some known steam turbines include seals that extend between tips of turbine rotor blades and inner surfaces of shrouds that surround the turbine blades. Known steam turbines experience several different phases of operation including, but not limited to, start-up, warm-up, steady state, shutdown, and cool-down. In at least some of such known steam turbines, for optimal efficiency, clearances between the turbine rotor blade tips and the inner surfaces of the shrouds should be kept as tight as possible during each phase of operation of the steam turbine. However, the clearances may vary as the steam turbine transitions from one operational phase to another. More particularly, each operational phase has different operating conditions associated with it, such as temperature, pressure, and rotational speed, which may cause changes in the clearances between steam turbine components, including static and moving components within the steam turbine.
In at least some known steam turbines, to prevent moving components from contacting static components and causing contact-related damage as the steam turbine transitions between phases of operation, the clearances are intentionally increased. For example, in at least some known steam turbines, cold, or assembly, clearances are set to be larger than required for steady-state operation because clearance gap closure is greater during transient operational phases, such as start-up, warm-up, shutdown and cool-down operational phases, than during steady-state operation. In addition, in at least some known steam turbines, larger clearances are provided to facilitate assembly of the steam turbine.